peteHVAC wrote:
>> peteHVAC wrote:
>>     
>>> I'm adapting a forklift motor to power my trusty 72 beetle.
>>> So far the mechanical part has been easy. The motor is a 36V 90lb
>>> monster and I'm guessing it can draw upwards of 500A. Controlling
>>> this much power has me stumped. I have the SCR control board from
>>> the forklift but no schematics. I have found a lot of sites selling
>>> controllers but not too much info on doing it yourself and looking up
>>> the components for the original controls hasn't turned up anything. If
>>> anyone can steer me in the right direction I'd be very grateful.
>>>
>>> Thanks, Pete
>>>
>>>       
>> take a look at the OSMC for a place to start.
>> some big power mosfets IRF1405's and some decent fet drivers and your
>> done ;->
>> easy lol
>> --
>>     
>
> Thanks for the link. Very nice I'm now a new member.
> The fets look nice too. I know what the datasheet says but can they really
> be run
> at that current? The leads are so small. It doesn't seem right 6 gauge wire
> hooked
> to a few little fets. I guess there is only one way to find out.
>
> I heard tell that measuring resistance of the motor and multiplying by
> voltage would
> give a close value of the lock rotor amps. any truth in this?
>
> Any good books about dc motor control?
>
>   
the FETs are only good for ~50A each, 75 is the package limitation.
with a fan though 50A per fet isn't unusual. At least for a robot.

direct resistance measurement is probably pretty ok for stall current.
don't forget to take into account the resistance of the leads in your 
test gear, and rotate the motor (SLOWLY) to see if it has less 
resistance in some places than others (as brushes make contact etc)
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